Driven by a growing demand by industry, governmental regulatory agencies and consumers for durable and inexpensive products that are functionally comparable or superior to metal products, a continuing need exists for improvements in composite articles subjected to difficult service conditions. This is particularly true in the automotive industry where developers and manufacturers of articles for automotive and construction materials applications must meet a number of competing and stringent performance specifications for such articles.
In an effort to address these demands, a number of composite materials have been developed, including glass mat thermoplastic (GMT) composites. Such composites provide a number of advantages, e.g., they can be molded and formed into a variety of suitable products both structural and non-structural, including, among many others, automotive bumpers, interior headliners, and interior and exterior trim parts. Traditional GMT composites used in exterior structural applications are generally compression flow molded and are substantially void free in their final part shape. By comparison, low density GMT composites used in automotive interior applications are generally semi-structural in nature and are porous and light weight with densities ranging from 0.1 to 1.8 g/cm3 and containing 5% to 95% voids distributed uniformly through the thickness of the finished part. The stringent requirements for certain automotive interior applications have been difficult to meet, however, for existing GMT products, particularly where such applications require a desirable combination of properties, such as light weight, good rigidity and good strength characteristics. As a result, a continuing need exists to provide further improvements in the ability of composite materials, including sheet materials, to meet such performance standards.